1. Field of the Invention
The present invention relates to an exchange-coupling film incorporating an antiferromagnetic layer and a pinned layer that are stacked, and to a magnetoresistive element, a thin-film magnetic head, a head gimbal assembly, a head arm assembly and a magnetic disk drive each of which incorporates the exchange-coupling film.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as areal recording density of magnetic disk drives has increased. A widely used type of thin-film magnetic head is a composite thin-film magnetic head that has a structure in which a write (recording) head having an induction-type electromagnetic transducer for writing and a read (reproducing) head having a magnetoresistive (MR) element for reading are stacked on a substrate.
MR elements include giant magnetoresistive (GMR) elements utilizing a giant magnetoresistive effect, and tunneling magnetoresistive (TMR) elements utilizing a tunnel magnetoresistive effect.
It is required that the characteristics of a read head include high sensitivity and high output capability. GMR heads incorporating spin-valve GMR elements have been mass-produced as read heads that satisfy such requirements. Recently, developments of read heads using TMR elements have been pursued to adapt to further improvements in areal recording density.
Typically, a spin-valve GMR element incorporates: a nonmagnetic conductive layer having two surfaces facing toward opposite directions; a free layer disposed adjacent to one of the two surfaces of the nonmagnetic conductive layer; a pinned layer disposed adjacent to the other one of the two surfaces of the nonmagnetic conductive layer; and an antiferromagnetic layer disposed adjacent to a surface of the pinned layer farther from the nonmagnetic conductive layer. The free layer is a ferromagnetic layer in which the direction of magnetization changes in response to a signal magnetic field. The pinned layer is a ferromagnetic layer in which the direction of magnetization is fixed. The antiferromagnetic layer is a layer that fixes the direction of magnetization of the pinned layer by means of exchange coupling with the pinned layer.
Conventional GMR heads have a structure in which a current used for detecting magnetic signals (that is hereinafter called a sense current) is fed in the direction parallel to the plane of each layer making up the GMR element. Such a structure is called a current-in-plane (CIP) structure. On the other hand, developments have been pursued for another type of GMR heads having a structure in which the sense current is fed in a direction intersecting the plane of each layer making up the GMR element, such as the direction perpendicular to the plane of each layer making up the GMR element. Such a structure is called a current-perpendicular-to-plane (CPP) structure. A GMR element used for read heads having the CPP structure is hereinafter called a CPP-GMR element. A GMR element used for read heads having the CIP structure is hereinafter called a CIP-GMR element.
A read head incorporating the TMR element mentioned previously has the CPP structure, too. Typically, the TMR element incorporates: a tunnel barrier layer having two surfaces facing toward opposite directions; a free layer disposed adjacent to one of the two surfaces of the tunnel barrier layer; a pinned layer disposed adjacent to the other one of the two surfaces of the tunnel barrier layer; and an antiferromagnetic layer disposed adjacent to a surface of the pinned layer farther from the tunnel barrier layer. The tunnel barrier layer is a nonmagnetic insulating layer that allows electrons to pass therethrough while the electrons maintain spins by means of the tunnel effect. The free layer, the pinned layer and the antiferromagnetic layer are the same as those of the spin-valve GMR element.
As a type of pinned layer of an MR element, there is known a pinned layer having a structure in which a nonmagnetic middle layer is sandwiched between two ferromagnetic layers that are antiferromagnetically coupled to each other, as disclosed in JP 2004-103806A, for example. Such a structure is called a synthetic structure, for example, and the pinned layer having this structure is called a synthetic pinned layer, for example. The synthetic pinned layer makes it possible to increase an exchange-coupling magnetic field of the pinned layer.
JP 2004-103806A discloses an exchange-coupling film in which an antiferromagnetic layer and a ferromagnetic layer sandwich are stacked and the direction of magnetization of the ferromagnetic layer sandwich is fixed. The ferromagnetic layer sandwich includes: a first ferromagnetic layer containing a ferromagnetic material having a body-centered cubic structure; and a pair of second ferromagnetic layers respectively formed on both surfaces of the first ferromagnetic layer and containing a ferromagnetic material having a face-centered cubic structure. The antiferromagnetic layer includes a random alloy and touches one of the second ferromagnetic layers. JP 2004-103806A discloses that the exchange-coupling film having such a structure allows the emergence of sufficient exchange-coupling energy even if the antiferromagnetic layer is thin. Furthermore, this publication discloses that a synthetic structure may be formed by providing a third ferromagnetic layer on a side of the other of the second ferromagnetic layers farther from the antiferromagnetic layer, with a nonmagnetic intermediate layer provided between the third ferromagnetic layer and the other one of the second ferromagnetic layers.
Furthermore, as examples of the material of the first ferromagnetic layer, this publication discloses Fe, an FeTa alloy containing 95% iron, an FeCo alloy containing 90% iron, and an FeCo alloy containing 50% iron. As examples of the material of the second ferromagnetic layers, this publication discloses Co, a CoFe alloy containing 90% cobalt, and an NiFe alloy containing 80% nickel.
JP 2003-060263A discloses a pinned layer having a structure in which a layer made of an FeCo alloy containing 50 atomic % iron is inserted between two layers each of which is made of a CoFe alloy containing 90 atomic % cobalt.
In the synthetic pinned layer mentioned previously, one of the ferromagnetic layers is disposed between the antiferromagnetic layer and the nonmagnetic middle layer, forms exchange coupling with the antiferromagnetic layer, and is antiferromagnetically coupled to the other one of the ferromagnetic layers. Therefore, to increase the exchange-coupling magnetic field of the synthetic pinned layer, it is important to enhance both the exchange coupling between the one of the ferromagnetic layers and the antiferromagnetic layer, and the antiferromagnetic coupling between the two ferromagnetic layers.
In JP 2004-103806A, although consideration is given to enhancing the exchange coupling between the antiferromagnetic layer and the layered structure of ferromagnetic layers, no consideration is given to enhancing the antiferromagnetic coupling between the second ferromagnetic layer and the third ferromagnetic layer that are the two ferromagnetic layers antiferromagnetically coupled to each other in the synthetic structure.
In JP 2003-060263A, no consideration is given to increasing the exchange-coupling magnetic field of the synthetic pinned layer.